The blast happened near Malpur village, just outside the city.
"It seems to be an old bomb buried long ago under the bush and garbage," senior police official Bani Amin told news hounds.
"A father and his son riding a
cycle of violence and a man travelling in a car were maimed in the blast," Amin said."The bomb disposal staff have collected some material from the blast site and are investigating. It could be an old hand grenade or a cracker," he added.